On a letter dated on Sept. 1, Aspen's birthday, President Donald Trump and First Lady Melania Trump wished her a happy 13th birthday.

"You are a brave young woman, and we are inspired by your strength and courage as you fiercely battle leukemia. Always remember that there are many people in your life who love, support you, and want to see you achieve your dreams," the letter said. "We are praying for your comfort and healing. May God bless you with the strength to stay strong. Keep fighting, and know that we are all on Team Aspen."